This proposal describes two coordinated studies of the endogenous and exogenous factors that influence the stability of protein and peptide pharmaceuticals. It investigates a novel degradation pathway, cleavage of the C-terminal Ser residue from the protein human relaxin when lyophilized in the presence of glucose(an aldehydic reducing sugar), and the well established route of degradation of Asp and Asn containing proteins and peptides, formation of a cyclic imide, to determine the roles played by primary sequence(endogenous) and environment (exogenous) in their degradation. These studies are significant due to emergence of many protein and peptide therapeutic agents brought about by the biotechnology revolution. A model pentapeptide representing the C-terminus of human relaxin will be used to reproduce cleavage found in the protein, study the requirements of primary sequence for cleavage, determine the generality of the requirement for glucose present, and study the significance of lyophilization in promoting this cleavage. A model peptide containing the cyclic imide intermediate formed in degradation of Asp and Asn containing proteins will be used to study the effects of neighboring hydroxy containing residues, Ser and Thr, the effects of pH, and the role played by buffer species as general bases in the aminolysis of the cyclic imide, the microscopic reverse(sharing the same transition state) of its formation.